Laser beam periodic-dot writing for fabrication of Ti:LiNbO_3 waveguide wavelength filters

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Abstract
A new laser beam (LB) writing technique that can provide dot lines of a nearly 10-μm period in photoresist, with a period fluctuation of less than 4 nm, is proposed and demonstrated. The dot period is also controllable with an accuracy of the order of a nanometer. The so-called LB periodic-dot writing has been successfully applied for definition of interdigital electrodes required for TE–TM mode conversion in Ti:LiNbO3 waveguide wavelength filters, in which the electrode period was nearly 10 μm at the center wavelength of the filter around 0.8 μm. The fabricated filter with a 5-mm-long LB-written interdigital electrode exhibited a filter bandwidth of 1.1 nm, which was in good agreement with the theoretical value. Eight filters with a period difference of 80 nm were then integrated on a LiNbO3 chip; as a result, the center-wavelength spacing between the adjacent filters was measured to be 5.4 ± 0.6 nm, as expected. Such fine control of the electrode period has thus become possible by the LB periodic-dot writing that was demonstrated. The writing accuracy is also discussed in detail along with the system description.

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